In the case of solar cells contacted on one side, both contact systems are arranged on one side for the out-flow of charge carriers generated by incident light at the junction of two semiconductor materials of different conductivity (absorber and emitter). The charge carriers are separated at the p-n junction between the emitter layer and the absorber layer and are delivered to the corresponding contact system. In the case of back-contacting, shading losses are avoided by a contact system, and therefore the efficiency of the solar cell is increased. Moreover, it is possible to provide further functional layers on the side of the solar cell facing the incident light.
By comparison with wafer-based solar cells, thin-film solar cells only require a fraction of the amount of semiconductor material and can be applied directly to an inexpensive glass substrate. It can be seen from most publications from the prior art that an Si absorber layer which is p-conductive is applied to a glass substrate by means of liquid-phase crystallization (see for example Amkreutz et al. in Solar Energy Materials & Solar Cells 123 (2014) 13-16; Haschke et al. in Solar Energy Materials & Solar Cells 115 (2013) 7-10; Dore et al. in EPJ Photovoltaics 4, 40301 (2013)), since this conductivity type is supported by the contaminants diffusing out of the glass substrate in the further method steps, in particular also by the liquid-phase recrystallization of an amorphous or nanocrystalline silicon layer. Likewise, a p-conductive absorber layer is also described in the thin-film solar cells proposed in DE 40 25 311 A1 or in DE 20 2005 019 799 U1. However, all these known arrangements according to the prior art do not achieve open circuit voltages of >600 mV.
Various contacting systems for back-contact Si thin-film solar cells are described in both DE 2005 025 125 B4 and DE 10 2010 007 695 A1. These solar cells have at least one absorber layer and an emitter layer arranged on the back which consist of semiconductor materials of opposite p- and n-type doping. Furthermore, a passivation/covering/anti-reflection layer on the side of the incidence of light is described in DE 2005 025 125 B4 for the thin-film solar cell. A buffer layer (a-Si:H) covering the contact structure on the back is provided on the opposite side of the absorber, i.e. the side facing away from the incidence of light, in order to improve the passivation of the interface between the emitter and the absorber.